tions of NGC 2346, and the staff of La Silla Observatory forassistance.

References

Aller, L. H.: 1968, lAU Symp. No. 34 - Planetary Nebulae (eds. O. E.Osterbroek and C. R. O'Oell), p. 339.

Cohen, M., Barlow, M. J.: 1974, Astrophys. J. 193,401.Cohen, M., Barlow, M. J.: 1975, Astrophys. Leiters 16,165.Greenstein, J. L.: 1981, Astrophys. J. 245, 124.

Kohoutek, L.: 1982, IBVS Budapest No. 2113 (see also lAU Cire.No. 3667).

Kohoutek, L.: 1983, Monthly Notiees (submilted).Kohoutek, L., Senkbeil, R.: 1973, Mem. Soe. Roy. Sei. Liege, 60 ser.,

t.V,485.Mendez, R. H., Niemela, V. S.: 1981, Astrophys. J. 250,240.Mendez, R. H., Gathier, R., Niemela, V. S.: 1982, Astron. Astrophys.

116, L5.Mendez, R. H., Niemela, V. S., Lee, P.: 1978, Monthly Notiees Roy.

Astron. Soe. 184, 351.Minkowski, R.: 1946, Publ. Astron. Soe. Paeifie 58, 305.Sehaefer, B. E.: 1983, IBVS Budapest No. 2281.

CCD Pictures of Peculiar Galaxies with Jets or ExtensionsH. Sol, Observatoire de Paris-Meudon

Astrophysical Jets

The phenomenon of "jets" seems to be rather universal inastrophysics. The astrophysical jets are seen in different~avelengths, from radio to X-rays. Their more general defini­tion IS "some emitting material weil collimated along a straightOr curved line". Such features appear on very different scales.J~ts having a length of the order of a megaparsec and of akiloparsec have been detected in different extragalactic sys­tems, respectively aso (e. g. 4C18.68; Gower, Hutchings, Ap.J. 253, L1, 1982) and radio galaxies (e. g. PKS 0521-36;Oanziger et al. MNRAS, 188,415, 1979). Jets of a few parsecs~ave also been suspected in galactic objects as the exotic

S 433, Sco X-1 and R Aquarii. Königl (Ap. J., 261, 115, 1982)even proposed to call jets the asymmetrical outflows whichappear in the models of bipolar nebulae, bipolar CO emissionlobes and aligned Herbig-Haro objects. Part of the galactic jetscould be miniature models of some of the extragalactic ones.

Jets in Galaxies

The presence of jet asymmetry is relatively frequent in thenuclei of galaxies. 50 % of the high-Iuminosity radio sourcesand 10% of the low-Iuminosity ones show a jet of a fewklloparsecs; all strong X-ray radio galaxies could have a jet;fnd the asymmetry of the VLBI structures is usually the rule:omalont, Workshop on Astrophysical Jets, Turin, 1982).

brecesslng radio jets in the centre of our own galaxy have alsoeen reported.Oifficulties arise if one tries to precise the first mentioned

general definition and to classify the different cases ofobserved jets, because they do not seem to form a veryhomogeneous class of objects. In particular, their spectralprOperties are not weil defined. A great number of jets is seen~nlY In radio, but radio-quiet jets exist too, as the optical jets of

GC 1097 (Wolstencroft, ESO/ESA Workshop on Optical Jets,~ 981). Other jets emit in both energy ranges, as the well-knownJet of M87. Strong optical emission lines can be present withoutany continuum counterpart (NGC 7385), although cases withan optical continuum and no lines (M 87) are also found, as weilas .Intermediate cases with both optical continuum and line~mlssion (3C277.3; Nieto, Workshop on Astrophysical Jets,

unn,. 1982). That diversity implies that the materials and the~adlatlon processes are not the same in all jets. The jet of M87~s probably made of a plasma which emits synchrotron radia­Ion, while some other jets could be a mixture of stars and gas.

The first duty of a theoretical model of jets is to propose a wayto break the usual spherical symmetry of many astrophysical

phenomena. Astronomers found different possibilities: rotationof a compact object, anisotropy of the ambient medium, two­body interaction, magnetic field, etc. Two main families of jetshave been suggested in the literature (i) matter ejected from anactive nucleus, as the M87 jet, or relics of such an ejection,(ii) tidal extension or bridge due to gravitational interaction orcollision of galaxies, as in the case of IC 1182 (Bothun et al.,1981, Ap. J., 247,42). Cases concerning both of those familiescould also exist, since for example the activities of galacticnuclei are expected to be enhanced during a collision event.

CCD Observations

Only a small number « 20) of optical jets in galaxies havebeen studied in some detail until now. But a greater number ofgalaxies have been suspected by visual inspection of Schmidtplates to have a jet and are c1assified in different catalogues as"jet-galaxy" or "galaxy with extension". Last year I made aCCO survey of 50 of those suspected cases in order to searchfor and to study optical jets in a statistical way. Some jetgalaxies already described in the literature have also beenobserved to be used as references: M87, 3C273, 3C120,IC 1182, PKS0521-36. At the same time, new information hasbeen obtained about them. The jet of 3C273 appears to becomposed of 3 regions which coincide with the radio wiggles.The westward 4 arcsec optical elongation of 3C 120 as weil asthe jet nature of the feature seen in PKS0521-36 are confirmed(Sol, Workshop on Astrophysical Jets, Turin, 1982.

The observations were made at the 1.5 m Oanish telescopeequipped with ESO's CCO during three different runs inJanuary, July and November 1982. The CCO was still in itstesting phase for the first two runs. Pictures of the galaxieshave been obtained in different colours, using a set of broad­band filters which covers the wavelength range of the CCOresponse, from 4000 Ato 1 micron (B and V Johnson's filtersand g, r, i and z filters described in Wade et al., PASP, 91, 35,1979).

As mentioned by Pedersen and Cullum in the Messenger ofOecember 1982, the CCO data reduction is not completelywithout problems if one wants to optimize the CCO capabilities.The first difficulty to face is the correction of several effects asthe discrepancy in sensitivity of the different pixels, the non­linearity of the cold columns and the interference rings due tothe night sky emission lines. A good and easy way to clean thepictures from those three effects is simply to divide the frame ofscientific interest by a correction frame, the offset and darkcurrent being first subtracted from both frames respectively.The correction frame is a picture of the night sky obtained by

33

Fig. 1: (a) First image of the galaxy NGC 1602 in the near IR (January 1982; 15-min exposure; z filter); (b) Image obtained after a pixel-to-pixeldivision of the image (a) by the night sky correclion frame. Note the peculiarity of the galaxy which presents a bright region with multiplecondensalions at the edge of a large diffuse component. A knotty jet hardly visible here is seen in bluer colour bands.

erasing all the objects contained in the scientific frames in onegiven filter during one observing night, and by adding the emptyframes obtained that way. The creation of that correction framedoes not consume any observing time, except if all the objectsof the scientific programme are very extended. (As long as wedo not know if standard correction frames can be made onceand for all and used by every astronomer, it might be a good

Fig. 2: This 15-min exposure (January 1982; 9 filter) of the galaxy ESO347 G22 shows several nuclear condensations. A large jet featurealigned with the central condensalion is cleariy visible (1 pixel = 0.471arcsec).

34

idea to incorporate in the programme of every observing nightsome rather empty fields, for example for detection of faintobjects, which can be used to build the correction frames.) Thephotographs 1a and b show the result obtained after such acorrection. The large-scale background variations were initially(photo 1a) of 10% in the central zone of the picture, and thefluctuations due to the interference rings of 2 % of the sky valuethrough the z filter. On the corrected image (photo 1b) theinterference pattern as weil as the cold lines are no more visibleand the background variations are reduced to less than 1%.

Of course the cleaning procedure outlined above cannotreduce the interference rings when they are due to emissionlines of the studied objects themselves. Other problems alsoremain, as the dead and hot pixels and the cosmic ray events,which can be cleaned by the use of software routines noWavailable in the MIOAS image-processing system (Banseet al. , The Messenger, March 1983). The charge transferwhichoccurs in the CCO during the picture read-out was not perfectduring the testing phase of the CCO. A few per cent of theelectrons corresponding to a stellar image were not weiltransferred and produce faint nebulosities around the stars.Although that effect does not seem to affect directly thephotometric results in a very strong way, it makes difficult theprecise determination of the sky background in the vicinity ofstars (Sol et al., submitted to AA, 1983). The charge transferis expected to be substantially improved by an adequatepreflash of the CCO chip before each exposure. The outflow ofcharges from the strongly exposed to the underexposed zoneswhich occurs in regions of high luminosity gradient would alsobe reduced by a preflashing procedure.

.­,

(a)

~ig. 3: The two upper (respective/y /0wer) pictures have been obtainedrom one exposure ofthe centra/ part ofthe ga/axy Mrk 314 (Ju/y 1982;15-mm exposure) in the i (respective/y g) c%ur band, seen with 2different contrasts. There is a bridge of matter between 2 mainCondensations, the southern one is very b/ue. Mrk 314 is /ike/y to be an~t~ractive case. The inner parts of 2 curved extensions are s/ightlyISlb/e at the upper and tower parts of the 9 exposures.

C From a qualitative point of view, the main superiority of aCD Image of one galaxy as compared to what is seen on a

Schmidt plate concerns the resolution of the brightest centralregi?ns of the galaxy. The sensitivity of the CCD permits astallstlcal approach while its dynamical range allows a simul­:~neous investigation of the faint extensions themselves and ofI~ parent. galaxies. It is therefore possible to roughly c1assify

~ the obJects of the sampie into different groups by using(I) morphological criteria on the extensions and on the parentralaxies and their nuclei, (ii) photometric properties as the jet­~-galaxy or jet-to-nucleus luminosity ratio in different colours.· mong the objects of the sampie, 10% appeared, on the CCDImages, to be possibly a superposition of classical astronomi­~~I Obj~cts, as faint stars or edge-on galaxies. The majority of· e obJects, however, remain very peculiar. 20 % are likely~~t~ra~tive cases with tidal extensions. 20 % show, besidest elr Jet-Iike features, multiple nuclear condensations, illus­;ta!~d by the photographs 2 and 3 and the Fig. 1. No jetb nklngly similar to the case of M 87 seems to have been found,· ut further Information as spectroscopic and radio data on theJet~eatures are necessary to draw more precise conclusions.

hanks should go to Massimo Tarenghi for initiating thiswork and to Preben Grosb01 and Andrezj Kruszewski who

H

(b)Fig. 4: /ntensity profi/es a/ong the line of the centra/ condensations ofMrk 314. (a) for the 9 c%ur band (b/uer); (b) for the i c%ur band(redder).

helped me to use the ESO data reduction system. I am alsograteful to the image processing group and photographers ofESO-Munich, as weil as to the staff members of La Silla.

New Optical and X-ray Observations Vield Progress inUnderstanding of an Old NovaH. Drechsel, J. Rahe, W. Wargau, Remeis Observatory Bamberg, Astronomical InstituteUniversity Erlangen-Fürth

d' Nova Aquilae 1918 was the brightest new star that wasIscovered since Tycho's and Kepler's supernovae in 1572

and 1604, wh ich reached a peak brightness of _4m and _3m,

respectively. On June 10, 1918, Nova V603 Aquilae wentthrough a sharp maximum of visual brightness -1 ';'1, followedby a subsequent steep decrease, making it an outstanding

35